1. Technical Field
This disclosure relates generally to a fuel injection control system for internal combustion engines which is designed to perform multiple injections of fuel into the engine and ensure the stability of burning of the fuel.
2. Background Art
Multi-injection systems are known which are engineered to spray fuel into an internal combustion engine (which will be typically called pilot injection) just before a main injection event to facilitate the ignition of sprayed fuel, thus reducing engine noise and consumed quantity of fuel. The pilot injection is to spray an amount of fuel much smaller than that in the main injection one or several times per stroke in the engine. The use of fuel that is low in cetane number may, therefore, cause the ignition delay to increase, thus resulting in a decrease in burned amount of fuel sprayed in the pilot injection or misfire thereof.
Japanese Patent First Publication No. 2009-299496 discloses a multi-pilot injection system which works to control a time interval between events of the pilot injections. Specifically, the multi-pilot injection system is designed to determine the pilot-to-pilot injection interval so that a spray of fuel, as produced by a latter one of two consecutive pilot injections, may be out of overlap with the cool flame, as produced by the former one, thereby establishing full growth of the cool flame to ensure the stability of burning of a desired amount of fuel in each pilot injection.
The above multi-pilot injection system, however, is engineered on the assumption that the sprayed fuel must be burned. Accordingly, when the ambient temperature is low, the atmospheric pressure is low, or the cetane number of fuel used is low, that is, when the ignitability of the fuel is low, it may result in lack in ignition of the fuel, which leads to an increase in unburned amount of fuel in the events of the pilot injection.